Adiabatic Losses Research Articles

Adiabatic Losses in Stirling Refrigerators

The Stirling cycle has been used very effectively in cryocoolers; but efficiencies relative to the Carnot limit are typically observed to peak for absolute temperature rations of about two, which makes it less suitable for low-lift refrigeration. The adiabatic loss appears to be responsible for poor performance at small temperature differences. In this paper, adiabatic losses are evaluated, for a temperature ratio of 2/3, taking into account the effect of phase angle between pistons, of volume ratio, of the distribution of the dead volume necessary of reduce the volume ration, and of the distribution of displacement between expansion and compression spaces. The study is carried out numerically, using an adiabatic stirling engine model in which cylinder flow is assumed to be stratified. Results show that the best location for the cylinder dead volume is on the compression side. Otherwise, all strategies used to trade off refrigeration for coefficient of performance are found to be roughly equivalent.

The nonthermal energy content and gamma ray emission of starburst galaxies and clusters of galaxies

The nonthermal particle production in contemporary starburst galaxies and in galaxy clusters is estimated from the Supernova rate, the iron content, and an evaluation of the dynamical processes which characterize these objects. The primary energy derives from SN explosions of massive stars. The nonthermal energy is transformed by various secondary processes, like acceleration of particles by Supernova Remnants as well as diffusion and/or convection in galactic winds. If convection dominates, the energy spectrum of nonthermal particles will remain hard. At greater distances from the galaxy almost the entire enthalpy of thermal gas and Cosmic Rays will be converted into wind kinetic energy, implying a fatal adiabatic energy loss for the nonthermal component. If this wind is strong enough then it will end in a strong termination shock, producing a new generation of nonthermal particles which are subsequently released without significant adiabatic losses into the external medium. In clusters of galaxies this should only be the case for early type galaxies, in agreement with observations. Clusters should also accumulate their nonthermal component over their entire history and energize it by gravitational contraction. The pion decay γ-ray fluxes of nearby contemporary starburst galaxies is quite small. However rich clusters should be extended sources of very high energy γ-rays, detectable by the next generation of systems of air Cherenkov telescopes. Such observations will provide an independent empirical method to investigate these objects and their cosmological history.

Spectral changes for local cosmic rays. II. The electron component and its interpretation

This is the second paper on the spectral variations of cosmic rays over the local region of the Galaxy and deals with the electron component. The EGRET data on cosmic gamma rays below 150 MeV from the Compton Gamma Ray Observatory are analysed in the manner of flux ratios of two energy bands over the sky. Combined with the results on the proton component from the first paper, and a measure of confirmation from the authors' earlier analysis of COS B data, they favour an interpretation that adiabatic energy losses and reacceleration by old supernova remnants are responsible for the observed spectral variations. Other possibilities are also discussed. They suggest that the directly measured cosmic ray spectrum at the Earth is probably not the same as the average over the local region of the Galaxy.

A new class of free stable doubly negative systems: First investigations on the SimO2−n series

Studies on several isomers of the C2O2−n and Si2O2−n series of dianionic systems are performed at the Hartree–Fock, configuration interaction, Mo/ller–Plesset perturbation theory and outer-valence Green’s function levels of theory. All examined C2O2−n systems are predicted to be unstable with respect to electron autodetachment. However, the analogues silicon systems Si2O2−n turn out to be electronically more stable than the corresponding carbon species. For Si2O2−4 which marks the onset of electronic stability in the SimO2−n series the influence of the basis set and electron correlation on the geometrical parameters as well as on the electron detachment energy are studied in some detail. The possibility of decomposition via fragmentation or adiabatic electron loss is discussed. A simple criterion to determine whether a given structure may represent a promising candidate for a stable dianion of the SimO2−n type is suggested.

A Stratified Flow Model for Adiabatic Losses in Regenerative Thermal Devices

A model has been developed for regenerative thermal devices such as Stirling engines and refrigerators, in which, while the heat exchangers are modeled as fully isothermal, the flow in the cylinders and dead spaces is modeled as adiabatic, one-dimensional, and stratified. Pressure is assumed to be spatially uniform, so that the two remaining conservation laws refer to mass and energy. It is shown that under the proposed assumptions, the conservation laws can be integrated in closed form with respect to the space variable, leaving only time integration to be performed numerically. As a result, the numerical integration is very cost-effective, sufficiently so that the resulting program can be used to chart large portions of the parameter space relatively quickly on widely available engineering workstations.

Relativistic hadrons and the origin of relativistic outflows in active galactic nuclei

We examine the hydrodynamic origin of relativistic outflows in active galactic nuclei (AGN). Specifically, we propose that the presence of a population of relativistic hadrons in the AGN "central engine" and the associated neutron production suffices to produce outflows which under rather general conditions could be relativistic. The main such condition is that the size of the neutron production region be larger than the neutron flight path cτ_n_ ~ 3 x 10^13^ cm. This condition guarantees that the mean energy per particle in the proton fluid resulting from the decay of the neutrons outside their production region, be greater than the proton rest mass. The expansion of this fluid can then lead naturally to a relativistic outflow by conversion of its internal energy to directed motion. We follow the development of such flows by solving the mass, energy as well as the kinetic equation for the proton gas in steady state, taking into account the source terms due to the decay of relativistic neutrons and adiabatic losses due to expansion. This process allows one to compute accurately the adiabatic index of the expanding gas, and in conjunction with Bernoulli's equation the detailed evolution of the bulk Lorentz factor. We further examine the role of large-scale magnetic fields in confining these outflows to produce the jets observed at larger scales.

Three-dimensional transport of cosmic rays in the heliosphere

The three-dimensional transport of cosmic rays in the heliosphere is reviewed. We report on results from our numerical simulations including convection, anisotropic diffusion, drifts, and both adiabatic energy loss and shock acceleration. Our model-heliosphere incorporates a wavy current sheet and Corotating Interaction Regions due to the increase of solar wind speed away from the current sheet. We are able to model the latitudinal as well as longitudinal variations, which latter appear as 26- and 13-day intensity waves. Our simulations for solar-wind speed, magnetic field, and cosmic-ray variations seem in general form quite similar to observational findings. Quantitative predictions depend on a number of physical parameters as the parallel and perpendicular diffusion coefficients, as well as on assumptions made on the structure of the heliospheric magnetic fields.

Stirling cryocooler model with stratified cylinders and quasisteady heat exchangers

A new one-dimensional model of Stirling cryocoolers is presented. A new rate-dependent heat exchanger model is coupled with our existing stratified, isentropic cylinder model. As before, the regenerator is modeled as isothermal, and pressure is modeled as spatially uniform. The heat exchanger model assumes that the timedependent mass flow rate in the heat exchanger is spatially uniform. This is a fair approximation if the heat exchanger volume is relatively small compared to the displacement. Under that assumption, the conservation laws for mass and energy can be integrated in closed form with respect to the space variable, in all the spaces, including cylinders and dead volumes, heater, cooler, and regenerator. This reduces the problem to a set of ordinary differential equations with respect to time, for pressure, velocity, and temperature, or entropy at the interfaces between the different spaces. We solve these equations numerically. Results are presented, which show that for typical cryocooler designs, losses due to irreversible heat transfer can be limited to a small fraction of the adiabatic loss. In contrast, the adiabatic loss remains roughly constant for all geometric designs with the same compression ratio.

Study of cosmic-ray H and He isotopes at 23 AU

view Abstract Citations (34) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Study of Cosmic-Ray H and He Isotopes at 23 AU Seo, E. S. ; McDonald, F. B. ; Lal, N. ; Webber, W. R. Abstract We have measured the spectra of H and He isotopes during the 1987 solar minimum with the cosmic-ray detector system (CRS) on the Voyager 2 spacecraft. By carrying out the measurement near solar minimum and at large heliospheric distances, the effects of solar modulations were reduced. In particular, the adiabatic energy losses were smaller, and these results from 23 AU over the solar minimum period of cycle 21 represent observations at energies not accessible from previous measurements near 1 AU. The modulated spectra with the diffusion coefficient constant k0 = 3.15 x 1022 sq cm/s (which corresponds to a solar modulation parameter of 360 MV at 23 AU and 500 MV at 1 AU) agree well with both our data at 23 AU and the previous solar minimum measurements at 1 AU. The measured H-1 and H-2 spectra are both consistent with the calculated spectra, using standard Galactic and heliospheric propagation models without invoking an anomalous hydrogen component. With the fixed modulation parameter of 360 MV, the mean pathlengths, source spectra, and cross sections were varied to study the effects of different input parameters on the spectra and relative abundances. At this stage of our work, we have not found any strong evidence from the low-energy H-2 and He-3 data that H-1 and He-4 should have a different propagation history, or different types of source spectra from the heavier cosmic-ray nuclei. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174604 Bibcode: 1994ApJ...432..656S Keywords: Cosmic Rays; Energy Spectra; Helium Isotopes; Hydrogen Isotopes; Interplanetary Medium; Nuclear Interactions; Abundance; Kinetic Energy; Radiation Detectors; Solar Spectra; Voyager 2 Spacecraft; Astrophysics; ISM: COSMIC RAYS; INTERPLANETARY MEDIUM; ISM: ABUNDANCES full text sources ADS |

Adiabatic losses in Stirling cryocoolers: a stratified flow model

A numerical model of Stirling cryocoolers is presented in which the machine is divided into spaces that are either fully isothermal or fully adiabatic. In adiabatic spaces, the flow is one-dimensional and stratified. Pressure is time-dependent, but spatially uniform. The model includes two conservation laws, namely for mass and energy. With respect to space, the conservation laws are integrable in closed form, so that numerical, iterative integration is required only with respect to time. The program implementing the proposed solution is fairly simple and very fast, because numerical integration with respect to space has been eliminated and replaced by the closed-form solution. Results are presented for two sets of assumptions regarding the expansion space. In both cases, the compression space is assumed to be adiabatic and stratified, while the heat exchangers are isothermal. Small cryocoolers may not have a freezer, in which case heat exchange occurs mainly in the expansion space which, in this situation, can be approximated by an isothermal model. For larger cryocoolers, the ratio heat exchange area/volume in the expansion space deteriorates; eventually, a separate freezer become necessary and the expansion space becomes nearly adiabatic. The adiabatic losses for these two cases are compared. Results are presented for temperature ratios between 0.1 and 0.95 and phase angles between 0 and 180°. Three different geometries are studied, in which the ratio of the swept volumes is varied between 0.5 and 1 † † The source code is available for inspection and non-commercial use as per the conditions specified in the program copyright notice. Please direct inquiries to the author .

Diffusive acceleration of electrons in SN 1987A

We suggest that synchrotron radiation emitted by electrons undergoing diffusive acceleration at the supernova blast wave is the cause of the reappearance of radio emission from SN 1987A in 1990 July. Making reasonable assumptions concerning adiabatic losses and the magnetic field in the preexplosion stellar wind, we find the light curve and spectrum which would be produced by a constant rate of particle injection occurring in a localized region of the shock front; i.e., in a clump or knot. Observations indicate that two such clumps have been encountered to date. From the observed delay in the switch-on of the emission between 843 MHz and 4.8 GHz we find a spatial diffusion coefficient for electrons of κ<SUB>normal</SUB>_ = 2 x 10^20^ m^2^ s^-1^. This value agrees with that found for the second clump and is substantially greater than the Bohm value. Estimating the magnetic field to be 10^-7 T and assuming the diffusion coefficient is constant leads to the conclusion that the shock encountered the first clump on about day 900 and the second clump on day 1190. From the observed spectrum we find the compression ratio of the shock responsible for electron acceleration to be ~2.7. This implies strong modification of the shock front which may be due to the acceleration of cosmic rays.

A theoretical study of linear carbon cluster monoanions, C−n, and dianions, C2−n (n=2–10)

A large number of carbon cluster monoanions, C−n, have now been detected by negative ion photoelectron spectroscopy. In addition, evidence for carbon cluster dianions, C2−n, as small as C2−7 has been obtained mass spectrometrically. In this research we report results of theoretical calculations of structures and energetics of formation of linear carbon cluster monoanions and dianions containing up to ten carbon atoms. A number of different electronic states have been investigated. Self-consistent field (SCF) theory, many-body perturbation theory, and coupled-cluster theory including triple excitations have been used with basis sets containing polarization and diffuse functions. Considerably larger basis sets have also been used in calculations on some of the smaller species. For the monoanions, the observed electron detachment energies and the even–odd alternation thereof are well reproduced by the calculations. For the dianions, the even numbered species are found to be more easily formed than the odd numbered species, in accord with the intensity pattern observed in the mass spectrometric experiments, and with the availability of partially occupied π orbitals. C2−10 is established to be vertically and adiabatically stable to electron loss, while C2−8 is found to be vertically stable but adiabatically unstable to electron loss. Improved calculations may be sufficient to make C2−8 also stable to adiabatic electron loss. C2−7 and C2−9 are both found to be unstable to vertical electron loss, although both have negative highest occupied molecular orbital (HOMO) eigenvalues and C2−9 is stable to vertical electron loss at the SCF level. The geometry changes resulting from the addition of two electrons are significant, especially for the even numbered clusters. Addition of two electrons to the partially occupied π orbitals of the latter leads to strong single–triple bond alternation, which may be rationalized by noting that the dianions are products of double deprotonation of HC2nH. Such an ‘‘accordion’’ mechanism may have a role in the ability of carbon clusters to conduct electricity.

Effects of geometry on edge states in magnetic fields: Adiabatic and nonadiabatic behavior.

In this paper we have studied the transition from adiabatic to nonadiabatic behavior of the edge states in the quantum Hall regime. The loss of adiabaticity due to strong changes in the geometry of the boundary potential is analyzed in different situations commonly present in experimental devices. When the Fermi energy is close to that of a bulk Landau level (LL), the edge state corresponding to such a LL remains uncoupled from the rest, even with a hard-walled boundary potential. So, at least for this edge state, the smoothness of the potential in both drift and lateral directions is not a necessary condition to maintain the uncoupling observed experimentally in different devices. On top of that, strong oscillations in the scattering properties have been obtained as a function of the various parameters defining the geometry.

Cosmic-ray transport and gamma-ray emission in supernova shells

The mixing and transport of cosmic rays accelerated by a pulsar inside an expanding supernova remnant are examined, and the resulting high-energy gamma-ray emission from nuclear interactions of these accelerated particles in the shell is investigated. Rayleigh-Taylor instability at the interface between a pulsar wind cavity and the inner supernova envelope is assumed to be the mixing mechanism. The analysis is applied to the model of Gaisser, Harding, and Stanev (1987), where protons are accelerated at the reverse shock in the pulsar wind. The instability time-scale is estimated from the dynamics of the pulsar wind cavity, and model the injection, diffusion, and interaction of protons in the shell. The resulting gamma-ray flux is lower than previous estimates due to proton adiabatic losses in the expanding pulsar wind. The protons mix and diffuse only into the innermost regions of the envelope before interacting. Energy-dependent diffusion causes the higher energy gamma-ray light curves to decay faster than those at lower energy.

Maximum energy of cosmic-ray particles accelerated by supernova remnant shocks in stellar wind cavities

view Abstract Citations (146) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Maximum Energy of Cosmic-Ray Particles Accelerated by Supernova Remnant Shocks in Stellar Wind Cavities Voelk, Heinrich J. ; Biermann, Peter L. Abstract The authors demonstrate that diffusive shock acceleration, balanced by adiabatic losses, leads readily to particle energies of ≥1015eV in the case of a supernova shock freely expanding into a stellar wind cavity. This process accelerates particles early on out of stellar wind material which is often enriched in certain elements (isotopes) and may thus contribute to explain elemental and isotopic anomalies in the cosmic rays. The authors speculate that the same process may produce particle energies up to 1019eV in the case of a supernova explosion in a compact binary star. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/185289 Bibcode: 1988ApJ...333L..65V Keywords: Cosmic Rays; Energetic Particles; Particle Acceleration; Shock Waves; Stellar Envelopes; Supernova Remnants; Binary Stars; Light Speed; Relativistic Particles; Stellar Winds; Astrophysics; COSMIC RAYS: ABUNDANCES; COSMIC RAYS: GENERAL; NEBULAE: SUPERNOVA REMNANTS; PARTICLE ACCELERATION; SHOCK WAVES; STARS: CIRCUMSTELLAR SHELLS full text sources ADS | data products SIMBAD (1)

Bursting Particle Acceleration in Radio Jets

This work follows on the papers by Henriksen, Bridle and Chan (1982) (HB) and by Eilek and Henriksen (1983). These papers introduced a comprehensive model of (hydrodynamic) turbulence driven Alfven wave, resonant, particle acceleration. Very similar ideas were introduced independently by Fedorenko (1980), but the details were sketchy and the universality of the resulting spectral index was not realized. Eichler (1979) has come closest to these ideas previously (again independently) in a very original paper directed at ion acceleration in solar flares. He includes a back reaction on the turbulent eddies however which requires an adhoc treatment and is probably unnecessary (we replace this by the Lighthill noise analysis: HBC) and he omits synchrotron and adiabatic losses. Moreover, the quasi-linear theory is not used in calculating the distribution function. Nevertheless, it is reassuring that the same intuitive physics, even to the self-similar universality, should arise independently.

Current Systems in Radio Jets

The structure of the magnetic field in radio jets is a topic of recent interest, especially due to the possibility that some high pressure jets are confined by a magnetic pinch. Several such jets have been found which cannot be confined by external cluster gas pressure, on which there are observational limits; nor can they be in free expansion, since they do not show evidence of adiabatic expansion losses. Recent radio interferometer observations of surface brightness and polarization allow the possibility of determining the magnetic field structure. In this paper I present some basic considerations of the current and field structure required if the observed jets are to be magnetically confined.

The inner heliosphere from solar minimum to solar maximum: Short- and long-term variations in the energetic particle population

Between 1975 and 1983 HELIOS 1 scanned the interplanetary medium between 0.3 and 1 AU 31 times. The observed variations in the differential and integral flux of protons and helium nuclei in the energy range from 4 to >50 MeV/n are characterized by large temporal changes in the intensities, moderate changes in the energy spectrum and changes in the gradient below the detection level (60%). During solar minimum conditions recurrent disturbances are caused mainly by corotating interaction regions. The onset of solar activity near the end of 1977, characterized by a large number of solar events, is accompanied by a monotonous decrease of galactic cosmic radiation. The successive reduction of the cosmic ray intensity to the level of solar maximum is discussed in view of the role of large transient disturbances as compared to processes as diffusion, convection, adiabatic energy losses and drifts.

Pressure sensitive “silica geothermometer” determined from quartz solubility experiments at 250 °C

Experimentally reversed quartz solubilities at 250°C and at 250, 500 and 1000 bars yield values of the logarithm of the molality of aqueous silica of −2.126, −2.087 and −2.038, respectively. Extrapolation of quartz solubility to the saturation pressure of water at 250°C results in a log molality of aqueous silica of-2.168. These solubility determinations and analyses of fluid pressures in geothermal systems indicate that pressure is significant when calculating quartz equilibrium temperatures from silica concentrations in waters of deep thermal reservoirs. The results of this investigation, combined with other reported quartz solubility measurements, yielded a pressure-sensitive “silica geothermometer” for fluids that have undergone adiabatic steam loss of t°C = 874 − 0.156P (log m Si(OH) 4 · 2H 2O ) 2 + 411 log m Si(OH 4 · 2H 2O + 51 (log m Si(OH) 4 · 2H 2O ) 2 where P is the fluid pressure in bars and m Si ( OH) 4 · 2H 2O represents the molality of aqueous silica measured in surface samples. The geothermometer is applicable to solutions in equilibrium with quartz from 180°C to 340°C and fluid pressures from H 2O saturation to 500 bars.

In situ acceleration in extragalactic radio jets

view Abstract Citations (70) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS In situ acceleration in extragalactic radio jets Bicknell, G. V. ; Melrose, D. B. Abstract An examination is presented of the extragalactic jet energy dissipated by large scale turbulence which is driven by a shear stability that does not disrupt the jet, hypothesizing that fluid theory should be used to treat the evolution of the turbulence. This permits the rate of dissipation to be estimated without a detailed knowledge of the process. It is found that Fermi acceleration causes dissipation at scale lengths of about 0.001 R, and that resonant acceleration plays no role. Consideration of the effect of Fermi acceleration, adiabatic losses and radiative losses on an initial power-law distribution with an upper cutoff shows radio emission extending up to at least 100 GHz to be possible, with no spectral index gradients being introduced by the acceleration. Using the present model in a study of its acceleration, the northern jet in NGC 315 is estimated to have a velocity greater than 5000 km/sec. Publication: The Astrophysical Journal Pub Date: November 1982 DOI: 10.1086/160444 Bibcode: 1982ApJ...262..511B Keywords: Energy Dissipation; Particle Acceleration; Radio Jets (Astronomy); Turbulence Effects; Adiabatic Conditions; Collisionless Plasmas; Flow Velocity; Rates (Per Time); Shear Properties; Shock Wave Propagation; Astrophysics full text sources ADS |